The invention relates to a process of preparing a conductive tin dioxide powder doped with antimony.
Recently a conductive tin dioxide (stannic oxide) powder has wide uses in the electric and electronic industries. For example, in certain types of electrographic recording media a conductive tin dioxide powder is employed as a principal material of a conductive coating layer.
A well known method for the preparation of a conductive tin dioxide powder is to fire a mixture of an antimony compound and an ordinary tin dioxide powder marketed as a chemical material thereby to dope a small quantity of antimony into the tin dioxide powder. The specific resistance .rho. of a tin dioxide powder obtained by this method becomes lower as the quantity of the doped antimony increases. However, the doping causes also unwanted coloring of the obtained conductive tin dioxide powder, and an increase in the dopant inevitably results in intensification of the coloring and lowering of whiteness of the antimony-doped tin dioxide powder. As another disadvantage, the particle size of a conductive tin dioxide powder obtained by this method depends strongly on the particle size of the tin dioxide powder employed as the starting material, so that the firing process needs to be preceded by pulverization of a commercial tin dioxide powder into very fine particles in order to obtain a conductive tin dioxide powder of a desirably small particle size.
It is known to form a conductive and transparent film of tin dioxide on a surface of a substrate such as of glass by spraying a solution of a tin compound, such as an aqueous solution of tin tetrachloride, containing a small amount of an antimony compound dissolved therein onto a heated substrate. In another known method of forming a conductive and transparent film of tin dioxide, a tin salt of an organic acid such as stannous acetate, stannous oxalate or stannous tartrate is evaporated together with a small quantity of an antimony compound so as to deposit antimony-doped tin dioxide on a surface of a substrate, for example, of glass. However, these methods are not useful for the preparation of a conductive tin dioxide powder.